For loudspeakers for use in various kinds of acoustic equipment, the technologies coping with conflicting demands of reduction in size and weight and improvement in performance caused by higher sound pressure and output have conventionally been pursued. Particularly for on-vehicle loudspeakers, weight reduction is strongly required to address recent global environmental conservation. For this purpose, a loudspeaker having the following structure is provided to meet these requirements. The loudspeaker includes a neodymium magnet having a high energy product in place of a conventional ferrite magnet, to downsize the magnetic circuit and thus considerably reduce the weight.
FIG. 5 is a semi-sectional view of a conventional loudspeaker of this kind. With reference to FIG. 5, cylindrical socket-shaped yoke 10 is separately formed into cylindrical outer peripheral part 10d and bottom part 10e and then joined together, to improve productivity. Magnet 11 made of neodymium is bonded to yoke 10. Top plate 12 is bonded to the top surface of magnet 11. Bonding yoke 10, magnet 11, and top plate 12 together forms magnetic circuit 13 including an annular magnetic gap therein.
Frame 14 made of resin has magnetic circuit 13 joined to the bottom surface of the frame. The outer periphery of diaphragm 15 is joined to the periphery of frame 14. Voice coil 16 is joined to the center of diaphragm 15 and fitted into the magnetic gap formed in magnetic circuit 13. Damper 17 is bonded to voice coil 16 to support the voice coil. Dustproof cap 18 is disposed in the center of diaphragm 15.
FIGS. 6A through 6C show how yoke 10 and frame 14 are joined to each other. FIG. 6A shows a bottom view of an essential part of yoke 10. FIG. 6B is a bottom view of an essential part of frame 14. FIG. 6C is a bottom view of an essential part of frame 14 having yoke 10 joined thereto.
With reference to FIG. 6A, along the outer periphery of the top end face of yoke 10 made of a magnetic metallic material, a plurality of notches 10a and protrusions 10b are disposed at a substantially equidistant spacing. Further, one of protrusions 10b has outward projection 10c. 
With reference to FIG. 6B, frame 14 includes clips 14a for receiving notches 10a in yoke 10 of FIG. 6A, and recess 14b for engaging with projection 10c of yoke 10 of FIG. 6A.
First, yoke 10 and frame 14 structured as above are combined so that clips 14a of frame 14 match with notches 10a in yoke 10. Next, as shown in FIG. 6C, yoke 10 is rotated so that protrusions 10b of yoke 10 are rotated under lips 14a of frame 14 and the clips prevent yoke 10 from disengaging from frame 14. Projection 10c of yoke 10 fitted into recess 14b in frame 14 during such rotation of yoke 10 forms rotation stop means. Holding protrusions 10b of the yoke under clips 14a of frame 14 in this manner prevents yoke 10 from disengaging from frame 14.
Providing slight tapering in clips 14a of frame 14 on the side of protrusions 10b of yoke 10 allows clips 14a and protrusions 10b to be compressed by each other. In this case, the above rotation stop means can be eliminated.
In the conventional loudspeaker structured as above, the yoke and the frame, i.e. the magnetic circuit and the frame, of an on-vehicle loudspeaker having reduced size and weight can easily be joined to each other.
For example, Japanese Patent Unexamined Publication No. 2002-10392 is known as prior technical information related to the above invention.
The above conventional loudspeaker has a weight considerably smaller than that of a loudspeaker having a magnetic circuit of a ferrite magnet. However, in recent commitment of the automobile industry to global environmental conservation, weight reduction is pursued on the order of grams. Particularly for a magnetic circuit combining metallic materials, further weight reduction is required.